The benzopyran derivative of Formula 1, whose chemical name is (2R,3R,4S)-6-amino-4-[N-(4-chlorophenyl)-N-(1H-imidazol-2-ylmethyl)amino]-3-hydroxy-2-methyl-2-dimethoxymethyl-3,4-dihydro-2H-1-benzopyran, is known as a compound having therapeutic effects for cancer, rheumatoid arthritis, etc. (Korean Patent No. 10-0492252). And also, the compound of Formula 1 can be prepared as an eye drop formulation based on a low-molecular weight material; and usefully applied to the prevention and treatment of macular degeneration, without injecting directly into the affected site as in the antibody injection therapy (Korean Patent Publication No. 10-2012-0112162).

A process for preparing the compound of Formula 1 has been disclosed in Korean Patent No. 10-0492252. Specifically, as shown in the following reaction scheme 1, the process for preparing the compound of Formula 1 comprises converting the olefin compound of Formula 4a to the epoxide compound of Formula 3a; reacting the epoxide compound of Formula 3a with (4-chlorophenyl)(1H-imidazol-2-ylmethyl)amine to obtain the compound of Formula 2a; and reducing the compound of Formula 2a to obtain the compound of Formula 1.

The compound of Formula 1 obtained in said process is isolated by filtering the reaction mixture obtained from the reduction to remove a solid, concentrating the filtrate, and then purifying the resulting residue with a silica gel column chromatography.
The present inventors have found that, as a result of performing the analyses on the compound of Formula 1 prepared according to the method disclosed in Korean Patent No. 10-0492252, the obtained product has low purity (less than 97 wt/wt % as an anhydrous form) and high water contents (more than 1 wt/wt %). Especially, the compound of Formula 1 prepared according to the method disclosed in Korean Patent No. 10-0492252 includes residual impurities (for example, organic impurities, inorganic impurities, residual solvents, etc.) originated from the preparation or rapidly-decomposed degradation products, and thus the purity thereof is not within a suitable range (for example, 99.0% or more) according to the Regulation on Drug Product Authorization of the Ministry of Food and Drug Safety, which causes the problem that it cannot be directly used as an active pharmaceutical ingredient. And also, the compound of Formula 1 prepared according to the method disclosed in Korean Patent No. 10-0492252 shows very high hygroscopicity. For example, the water contents thereof are increased to 2.30 wt/wt % in 1 day under the accelerated condition; and thus strict control thereof is required. In addition, the product itself obtained immediately after the preparation has also high water contents, which is not suitable for use as an active pharmaceutical ingredient.